Mark global-interface-listing.html as Slow.

It takes 1-3 seconds on Release and ~10 seconds on Debug.

TBR=brucedawson@chromium.org
BUG=647192
NOTRY=true

Review-Url: https://codereview.chromium.org/2342803002
Cr-Commit-Position: refs/heads/master@{#418832}

third_party/WebKit/LayoutTests/SlowTests

@@ -302,3 +302,4 @@ crbug.com/623798 paint/images/animated-gif-last-frame-crash.html [ Slow ]
 crbug.com/606649 fast/dom/gc-dom-tree-lifetime.html [ Slow ]
 
 crbug.com/647192 fast/css3-text/css3-word-break/word-break-all-ascii.html [ Slow ]
+crbug.com/647192 virtual/mojo-loading/webexposed/global-interface-listing.html [ Slow ]